Scale insects are among the most serious pests of shrubs and trees in the landscape. Scale insects fall into two groups - armored scales and soft scales. The armored-type is what we usually call "hard scales." Both types of scale insects secrete a cover which protects them from weather, predators, and insecticides. You can identify the scale by the type of cover it has and other characteristics. Scale identification may be important in selecting the proper control.

Armored Scale: The scale insect's cover is separate from the body. If you flip the cover off an armored scale, the insect beneath it will remain intact. Armored scales feed on the contents of plant cells and do not produce honeydew.

Soft Scale: The scale insect's cover is part of the skin of the insect. Flipping the cover of a soft scale tears the insect's body apart. Soft scales feed in the conducive elements of the plant, the xylem and phloem. Like aphids and whiteflies, the soft scales produce lots of honeydew. This coats the foliage below with shiny, sticky liquid and supports the growth of sooty mold.

There can be as many as five or six generations of scales per year for some species, but most have just one or two. Some soft scales give birth to living young, but most lay eggs that hatch into mobile crawlers. The crawlers move out from under the cover of the female and settle down to feed on leaves or stems. Once settled, most lose their legs and do not move again. Others like wax scale and cottony cushion scale, retain some degree of mobility throughout their lives.

The cover of scales is secreted beginning with the first molt and provides very effective protection for the insects from weather, natural enemies, and insecticides. Scales can be small and hard to see, like obscure scale, or large and conspicuous like wax scale. The main effect on infested plants is a gradual weakening that can lead to thinning of the plant's canopy, die back, and eventually death.

Contact insecticides are effective against young crawlers, but less so against later stages. Systemic insecticides can be very effective against soft scales but only a few are effective against armored scales. Horticultural oils are also effective, as are insect growth regulators. The biggest challenge is usually identifying scales as the problem.

If you think you have a scale problem, break off a piece of infected plant tissue and bring it into the office.

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